Linear electromagnetic machines are known that have two parts that move relative to each other in a sliding direction. At least one of the parts extending in the sliding direction includes active elements, each made up of a succession of portions having different magnetic properties.
In variable-reluctance machines, the portions of each active element alternate between ferromagnetic portions and non-magnetic portions. In permanent-magnet machines, the active elements of one of the parts comprise portions that alternate between ferromagnetic portion and non-magnetic portions, while the active elements of the other part comprise magnetized portions that alternate between portions magnetized in a first direction and portions magnetized in a second direction opposite to the first.
The two parts are placed to interact electromagnetically, one of the parts being associated with means for generating a magnetic field. Magnetic-field generation causes magnetic forces to appear that tend to move the parts relative to each other in the sliding direction. Alternatively, the machine may be operated as a generator by imparting a relative movement between the two parts.
In a first type of electromagnetic machine, the portions making up the active elements are in the form of plates or blades. The active elements of the two parts are parallel and form respective interleaved combs such that an active element of one of the parts extends between two active elements of the other part (naturally with the exception of the outermost active elements).
In an embodiment shown in FIG. 5 of document FR 2 588 133, the portions forming the active elements of the movable part are subdivided into two sub-portions extending on either side of a central support that holds the sub-portions at one end thereof and that takes up the magnetic forces to which the portions are subjected. The portions forming the active elements of the stationary part are likewise subdivided into two sub-portions, each being held via one of its ends by an external support.
Those supports are complex to fabricate and they receive each of the sub-portions via one end only, which means that the sub-portions are cantilevered out and that they are therefore subjected to stresses that tend to separate them from the supports that receives them. In addition, the end of each sub-portion that is engaged in a support is not in magnetic interaction with the sub-portions of the facing active elements, and those ends therefore do not participate in the operation of the machine. In addition, the presence of central supports and of external supports increases the overall size of the machine. The supports do not participate in the magnetic interaction between the active elements, so they take up precious space and tend to limit the volume power density of the machine.
In a second type of electromagnetic machine, as illustrated in the article “Actionneur linéaire synchrone machine à aimants permanents multi-tiges” [Synchronous linear actuators with multiple-rod permanent magnets], presented to the colloquium “Electrotechnique du futur, SUPELEC, Dec. 9-10, 2003”, the active elements of the movable part are in the form of rods and comprise cylindrical portions threaded onto a central support. The central support holds the portions and mechanically takes up the magnetic forces to which the portions are subjected, and it stiffens the rod.
As with plates, the central support does not contribute to the magnetic interactions and it occupies precious space, tending to limit the volume power density of the machine.
As suggested in document FR 2 588 133, it is possible to omit the support and to bond the portions of a given active element to one another by adhesive or by brazing. Nevertheless, that method assumes that the portions are mutually adjacent and that they are suitable for being bonded together by brazing or adhesive. The magnetic forces are then transmitted mechanically in traction through the bonds made in this way, which is not ideal from a mechanical point of view.